Note: Descriptions are shown in the official language in which they were submitted.
~86g~
SPEC IFICATIO~
Field o the I~ve~tion
-
The preser~ ven~ion relates to the field of powder
mqtallurgy and, more part~cularly~, to the fabric~ion oi h~gh
strength metal bodi~s ~rom ~tallic powdersO T~ :inv~n~ion is
hu~ dir~3cted ~o a methQd of fabrica~ing ~uclh powder metallur~
gical ~truc~ures and ~o a me~hod of operatitlg equiRment for
this purpose.
In the fabriGatiorl of maT~y ~?tallic articles ~or rRsdern
technolo~yg i~ be~n found ~o be ad~antageous to u~ilize
powder rnetallurgy, eithq~ becaus~ thE Ic~tals which are used
ca~llot coTI~e~iently b~ shaped by earlisr co~v~T~tlonal machirl-
iTlg cec~nique~ oJ; becau~e ths ~ es ar~ such t~at t~0 earli@r
cas~ g and ~chlnitlg tec~oLogy is in~ff~ctive. In addi~ion~
it i~ po~ible by powder metaLlurgical tel~i~es to produc~
~odie~ w~lch can h~v~ so~e d~gree of porosityS, a~ adva~tag~
wh~n flu~ds may be taken up or dispens~d by th~ body" or wh~re
t~ inish~d artlcl~ ~hould ha~7e a l~ss~r density tlhan that o~
20 the ~slid elemsntal metal or allo~O
Powder metallurgical ~c~miques also may b~ used tc
a~van~agQ w~ t~ composi~ion of the body i such ~hat an
equ~al~t compositio~ cannot b~ mad~ by casting or th~ lik~;,
In g~e~al~ the powder m~tallurgical approach r~quir~s
the shaplng o a ma5s of m~taLlic powder and the sub~quen~
or cont~mporall~ous stabilizatiorl o;f th~ shaped mass ~v ~hat
t~ desired ~tr~n8th and shap~ ret~nt~7ity can be achiev~du
~L~86~
In t:hQ usual approach" a inely divid~d met21 powder in a
10wable forrn iis poured lnto a cavity havlng ~h~ hape of the
d~ired body and is compac~ed,, c:ompressed or o~herwi~e detlsified
in thi~mold to pr~duce a so~called gr~en compac~
T~ gre~rl compact i~ ~heTI sin~ered to produce a ~truc-
~urally s~abl~ body w~ich may be used as such or which can be
~ormed" den~ified, shaped or altered as to i~s physical and~or
ch0mical proper~ies to yield the ultimat~ objec~O Typi~cal of
the processs~ to which th~ si~ered body call be sub;i~c~ed are
~0 variou~ pressin~ and forging techniques which alt~r ~k~ grain
~i~e and stre~gthen ~he body~
ThQ sin~ri~ sl:ep require~ fusion of ~h~ mu~ually con-
tactiTIg metal par~cl~s of the green ca~pac~ so ~hat ths par-
ticles partially merge wlth one another at their contact point~
or surfa~es~ the sintQring temperature being below ~h~ meltirlg
poirat at which. the particles are coTIverted into a liquid phase"
Subseque~t or during siLnt~ring, ~h.e body can b~ d0nsi~ied
by t~ app~ication of pressure~
Th~ sinterad body is gaTI~rally por0us and ca~a be used a~
20 such if it has sufficieTIt str~ngth, or can be s~ec~ed ~o the
~urth~r densificatlon or str~ngtb~ing steps m~ntioned, th~se
steps ge~rally invc)lving a reduc~iQrl in the porosity of t~
bodyO
The fur~her compac~on after sin~rin$ ca~a be effected in
th~ cold ~tate o~ the body or in a wann os~ ~o~ condi~ion t~re~
of arld i~ i~ also possible wi~hin tlt~ cont~xt of co~ventional
powder metallurgy, to ~ubject a previously si~tered and d~nsi~
~i~d body to a :Eurther sint~rin~ step at an elevated t~mp~ra~
ture ~o caus~ ~ve~ :further s:oalescenc~ oiE the par~ioles
30 at thelr incerfaces ox mod~ficaticn of i:he grain structure~
--2--
Th~ ~ar~ing powder can b~ fr~e from a binder or oan b~
c~bined wi~h a binder.
~ atllrally9 th~ ~e~n "green" ~ here u~ed in ~h0 sense in
which ~hi~ rm has b0en employecl in the powder metallurgical
field here~ofor~ no~ re~er to an ~ject having a greerl color~
ation3 but rath~r to refer to t~ co~rent compact in its pre-
sint~red sta~e as one in which th~re ha~ b~en no signi~cant
coalescence of the mu~ualJLy contaoting surface~.
A~ d~scr~bQd in ~he
~ , 1975,, Vol, lJ 3 Nt)~ 3, Pages
~09 to 2~0, t~ m~tal powder car~ b~ s::omlbined wi~h an organic
binder which, in ~his publication, is p~e:Eerably saccharose.
The biLnder-containing me~al~powder mas~ can be densified in a
mold o~ the Sh~lp9 o:l~ the artlc1e to b~ made by simple vibra-
t ~orlO
Th~ resulting gre2n compac~ ls ound to h~ve insufficient
gre~n ~re~gth to enable it to be r~mav~d ~rom ~he mold and to
be ma~ipulated as desired. Herlce at l~a~t partial sinterlng
is effected wh~le th~ grsen coIapac~ ig wi~hin ~he ~oldO
The sin~ering ~:~ green compac~s withirl th~ mold ~o that
they oan ultimately be withdrawn and h~ndled~ has ~gnlficarlt
disadvan~ages~ ExperiL~ncs has ~howrl3 for exa~ple, ~ uch
sintered bod1es do not have suficient1y homog~rleou~ and repro-
ducib1e p~ysical parameters such ~s den~ity~ s~reIIg~h and poro~
~ty or por~ vclumeO
Th~ poroæ1t~7,, density and strength ar~ al~o adverse1y
af~cted by the u~e o:E uIlr~duced m~tal powder~ which t~nd to
interfere with si~texingO Th~ physical param~ters are thus a
func~iorl of th~ degree of sirlt~ring which caa~ varV from body to
bGdy even wh~re ~ssentia1ly identica1 process conditions are
m~in~ained.
~36~
In fact,, ~h~se parameter~ can vaL^y mark~dly from place ~o
p:Lac~ ev~xi wi~hLtl a given bod~3 especialiLy if" in ~h~ forrnation
of th~ green cc~mpact, the compacting has llot been uni~orm~
T~ sam~ applies or carbonizatioll parame~ers wh~n a
carb :3ni~ation i~ carrîed out in addition co the sintering.
Thi~ is partîcularly the cas~ W~ll the powder me~allurgical
opera~iorls are carried out in the abs~nce sf binders ar with
~m~ll quarltities of biTlder or ~he sin'cer~d body ultima~ely has
a plurality o dif~erent cro~s sectio~sO
In a preferred mode o~ producing ~in~er~d metal bodies5
a reduced metal powder wi h he :lowe~t possibl~ oxygen content
is gensrally ~mp:Lcyed although such m~tal powd~rs arQ compara-
t~ely exp~I~siveO 5uch powders are ~ha.ped by pr~p~3ssing with
el~vated press pressur~s lllto the green compact and sint~red
to produc~ a body which can be subsequ~nJsly 'created~ shap~d or
handledO
I~ will thus be appreciated ~hat earlier techniques in ~3
fa~rication by powdPr m~tallurgy of sln~er~d metal bodies ~ava
generally involved a tradeo:Ef whereby mor~ ~perl~ive rQstal pow~
20 ders were required or t~e processing tec~ology was more com~
plexO
Irl a fiqld r~mQ~e frQm powder m~allurgyD narnely in the
productivn of sand molds for moltell m~tal casting;, it is known
to produce a mold cavity from mold sand and oundry sand bind~rs.
Such ~nolds ran b~ provid~d with so-called saxld core~ which also
generally compri~e foundry ~and and binders de~igned to pro-
vide the core which is used to :form an int~rnal cavi y hole
or recess in the ca~ting,, so that t~ core poss~sses a cer-
~ain degre~ of int~grity ~uring th~ castin~ opera~ion but ye~,
3~ as a r~sult of the heati~g during th~ ca~ting proce~s, lo~es
this integrity in whole or in part and becomes fran~ible or
otherwise easily remavable from the hole~ recess or cavity
onc~ ~he cas~ing is removed rom the moldO
Such ¢or~s~ whil~ hav:Lng suf~icl~nt green stren~sth to re~
sist th~ pressure o ~ ms:~lten m~a:L dur~ng ~he casting oper~
atioTI~, los~ lntegrity UpOTI ~2atiIIg during the casting processb
Thl5 iS also ~ a~e with more recently deYeloped foundry
sand bi~ders of a synth0tic resin ba~e~
Sand cores o~ ae aforedescribed type can bs produc~d,
as is well kT~own in i:he foundry :Eield~ on cor~ fo~ning ma-
chines which have mechaliz~d ~he prs~duotiorl of ~uch cor~ for
~oundry purposesO
~er~tofore such machine~ hava been us~d exclusi~7ely or
th~ productio~ ~f bodie~" nam~ly the sand cores9 which in~
ten~onally have diminished integrity cmd str~ngth upon b~ing
subjected to elevated ~emperatur~, e~gO during cas~ingO Such
machines have not, a.s i~ is known, ev~3r been ussd :tn ~ abrl-
ca~ion of ang bodi~s othsr ~n ~arld cores for :Eoundry purpo~e~
~nd c~rtainly ha~ flO~ ~ound appl~cation i~ 'c~ powder ~etal-
lurgical field w~ich, by cont:ra~t with foundry application6 of
~and cores~ recluires that a h~ated body gain in streng~h as a
result of th~ heati~g operation9 eO~gO sin~ring~
It~ fact" th~ produstion of ~and oores for oundry purposes
and powder ~tallurgical ~cecknologies ar~ vastly difer2TI~ and
~v0 li~tle i~ any s~o~on bas~s~ dealing with different pro~lems
and differqrlt approac~s to ths ~olution~ thereof/ Th~ f~eld
oiE m~tal s~apillg has long recog~ized a ~evere dichotomy bet~
weQn worl~er~ with th~ powder n~tallurgical approach and with
~oundry exp~rt i5e 0
~rom Germall patent docume~ts - Print~d ~pplication DE AS
lg64 4269 it is k~owrl t~ pr~vide sinter~d metal bodies using
~e r~l~tall~c powd~r in co~binati~n with an orgallic powd~r in
~5-
3;~1D
the fvrm of a hardenable re~n, generally of ~e epoxy typ~
t~ mixture of ~ch~ powder and ~he resin ~onnirlg a ~Elowabl~ mass
which i~ poured :Lnto a c~vity to produce a body analogotls t(3 a
gree~a compact which ls th~n harde~ed in ~his cavityO
Th~ ~haped compact can ~hen be subjected ~o a mult~:tage
heat ~reatm0nt, ~he firs~ stag~ of which involves the compo~i~
tion o Sh~ bind~r, whlle further ~:ages result in sinterirlg
of th~ metal particles of the body toge~:~er~,
I~a this approac~ as with the other po~der met:allurgical
~0 tecbrlique~ described ~ homogenei~y or isotropy of kh~ p~ysi-
cal phanomena in th~ sin~Qred body is no~ su~Efici~n~ eO the
un~forml~y ~hroughout ~he body leave~ much ~:o be dssired and ~he
proce~s may not be reproducibl~ in t~ fabricatioll in a number
o~ such bodies which should be identical as to ~h~s~ phy~cal
prop~rties 0
Apparell~ly ~he homogelleity arld reproduceability deviat~s
from des:lred levels aæ a result of the nonuniormity in the dis~
~ribut~on of tl:~ m~tal powder in t~ fl~wable biader whi~h, in
turn7 may be af~cted by th~ way ln which the ~lowable mass is
20 poured lnto the cav~ty or t~ co~ditions under which ~uch pour-
ing takes place~,
In genarala, as to c~ventional powd~r met:allurgical tech-
nique~ knowr~ her~tofore, a ma~or pr~blem has resided in th~ :Ln-
ability to produ ~ articles of an Q~tremely high l~vel oi~ h~o-
geneity ~n a fully reproducible a~d econolnical mamler e~pacially
when ~hs bod~es to b~ ~orm~d h~v~ di~ferent cro5~ sactionsO
Oe ~ I~e~
Xt i~ t~ prinelpal ob~ct of ~ present i~7~ntion to pro~
viid~ a~ impro~7ed method o~ ~aking sintered metal bodies wh~reby
30 ~1ae disadvanta~e~ of th~ ear~ier t~c~ ques in th~ powder metal-
lurgical art can be 0~7iatsdO
-6-
:~8~
Another ob~ect of the invention is to provide an im-
proved method of making metal bodies of a high degree of homo-
geneity in a reproducible and economical manner, even in the
case of bodies having portions of different cross section.
Yet another object is to provide an improved powder
metallurgical process which can be used to form intricate metal
bodies in a simple and convenient manner.
Another object is the providing of an improved method
of operatiny a machine which enables sintered metal bodies to
be made with practically homogenous physical parameters even
when such bodies have differing cross sections.
These objects and others which will become apparent
hereinafter are attained, by a method wherein a particulate mass
of a metallic material is shaped into a green compact by the
kinetic displacement of the metal particles into a shaping form,
the resulting compact being removed from this form and then
being subjected to a sinterin~ operation. It was found that by
introducing with comparatively high kinetic energy the particu-
late metallic mass into a shaping form, it is possible to
produce a homogeneously compacted green body which has suffi-
cient strength to enable it to be handled, removed from the form
and sub~ected externally of the form ko sintering.
More particularly, this disclosure provides that the
flowable metallic particle mass is shaped into the green compact
in a conventional core-forming machine which, in spite of its
designation, is here used not to make casting cores but rather
to produce green compacts to have sufficient green strength to
enable them to be removed from the forming cavity and to be
subjected to sintering.
-- 7 --
~,0,
36~3~3
Surprisingly w~ile such machi~s have be~n us~d in ~h~
past in t~ foundry lndustry to make coras o intentionally
limi~d integritya, ~h~ æame machines can be utiliæed with
powder metallurgic:al materi!als tn produce bodles which ulti~
ma~ly are of high s~reng~ch and dens~ty and which can be sub-
jec~d af~er s~nterlrlg9 i f desired5, ~o additioI~al processiT~ga
.g~ by forging to increase Sl::rQrlgth~ changQ 'ch~ shape or alte~
grain~crys~allirl~ paraEne ters O C~// S C/O
ccordiIlg to a fea~ur~ of ~he ~}, me~allic~
powder masæ can iI~ lude a bi~dqr al~hough binder-~ree operation
is also po5Sible!o In a preferred e~bodimen~ o~E ~he invention~
~h~ m~alllc powder i5 mixed wi~;h a syn~l~tic resin binder ~
forms the ~lowabl2 mixture whie~a is ~haped into the green com-
pact on a core~orming machine while a v~ri~t~7 o~ syn~hetic
resin lbi~ers can b~3 us~d~ only ~s~ential that thQse
bind~r~ be ~ompo~it~ons ~hich are e~ec~iva :~or powder metal-
lurgical purposes" e~g. dec~mpose upon ~intering~ allow the
m:ix~ur~ to be pourable and enable the mixtur~ to b~ handled i~
a formi~g machine of t~ core-~ormi~g mac~ine typeO
2~ Tl~ orgaaic binder" ~urp~isingly" n~ed not b~ e~clusive
ly o a ~ype ~re~ofore dev~lop~d ~or the po~der m~tallurgical
art but can be a co~ntional oundry sand binder of t~e syn-
~h~tlc resirl typ~ ~nd furth~r t~ proportions o~ ~he me~allic
powd~r on th~ binder ca~ correspo~d to the proport~on of ~and
and bind2r u~ed in the production of foundry cores on such
mac~alnes O
AdvaIItageou~ly9 the organic binder i~ a pherLolic res~n
bi~der whlch can be used in an amownt of les~ than lOP/o by weight
o:E th~ mixture~ pre~erably in an amouat ~ about 1% by weightO
30 The ouTIdry sandb~nd~rs o th~ synthstic r~sin typ~ can be used
in 3pite v ~h~ act t1~t~ upon h~ating~ th~y lo~e their binder
~6~
capabilities and permit collapse of sand cores, because the
shaped compacts here described are heated to sintering tempera-
tures and thus re~ain their strength and integrityD
It is possible, using a machine of the core~forming
type, to fabricate green powder metallurgical compacts of
complicated shapes and zones of markedly different cross sec-
tions with a uniform density and degree of compaction completely
without segregation phenomena, i.e. phenomena whereby the metal
powder is separated from the synthetic-resin binder and vice
versa. As a result khe sintered body and the ultimate shaped
member have completely homogeneous physical parameters.
Surprisingly, the green compact has an unusually high
green strength so that it can be handled free from the shaping
form and sintered also without retention in the form and there-
by also reducedr carburized or decarburized.
For compaction of the sintered body use can be made of
hot or cold compression techniques which are themselves con-
ventional in the metallurgical arts for the production of
sintered bodies and other ob]ects. An important advantage is
that objects can be made by the present process which could not
be Eabricated as sintered bodies or by powder metallurgical
techniques heretofore or cauld only be fabricated by other tech-
niques at high cost~
The method can utilize any conventional metal powder
as the starting material for the produckion of sintered bodies.
In general the method can also use mixtures of different metal
powders or metallic powders, i~e. powders containing a high
pxopor~ion of metal bu which may also contain metal oxides or
the like.
_ g _
~6g~
Instead of being restricted exclusively to reduced
metal powders which are of high cost and are characterized by
their freedom from oxide films or the like, unreduced metal
powders or mixtures of reduced and unreduced metal powders can
be used.
When the metal powder used as the starting material is
unreduced metal powder or contains a quantity of unreduced metal
powder, the green compact is preferably sintered in a reducing
atmosphere and the reduction is customarily carried out to re-
duce all of ~he oxide presen~ or all of the oxide accessible tothe reducing temperature.
It is sufficien~, however, that the reduction be con-
centrated at contact points between the particles in the green
compact and this can be promoted by utilizing an organic powder
which, containing carbon, promotes reduction or contributes ~o
the reducing action.
When, a partly reduced metal powder is used, neither
the body sintered from ~he green compact nor the compacted or
otherwise shaped products have their physical char~ct~ristics
affected by a residual ox~gen contact. Any residual oxygen con-
tent is found to ba totally ineffective and for example does not
have any deleterious effec~ on the subsequent compaction shape.
Another important advantage is that intricate shapes
can be fabricated with portions of different cross section with
out any transfer material between this section during the
sintering operation.
The method can be carried out with a binder from a
starting powder which can be introduced into the compact-shaping
form and subjected, prior to introduction into this form, to a
3a physical and/or chemical binder-promoting treatment.
-- 10 --
:~86~2~
For example with a reduced metal powder, the binder-
promoting treatment is an oxidation which forms an oxide film
on the particles which acts as the binder upon fusion linter-
melting) of the oxide films and the metals of mutua'ly contact-
ing particles during the sintering operation.
The process can utilize practically any metallic parti-
culate material with a minimum of preparation of the powder
charge. It suffices, for example, to recover the powder by
sifting after separation of particles having a size of 600
microns and more. The remainder of the powdered char~e, includ-
iny oxidic dust from the dust removal or air cleaning facility
can be used for producing sintered objects.
It is also possible to mix the starting powder from a
collection of alloying elements in the orm of metal powder,
prealloying powders or metal compou~ds such as oxides, sulfides
ancl carbonates and natural minerals. ~ven dusts, slurries and
other metallurgical wastes, to the extent tllat they consist pre-
dominantly of metal, can be used either alone or as admixtures
to the aforementioned powders. The term "metallic powder" as
used herein is intended to comprehend all of these starting
materials.
Utilizing the technique described, a green compact is
produced which has the desired quantity of powder in each ele-
ment of volume and uniformly through any cross section, The
compact form can be of simple construction since its filling
does not require elevated pressures and the form need not be of
the supportable type constituted by a ram and by segments.
Nevertheless the sintered body has a sufficiently high
density strength that even with further compression thereof ma-
terial transfer from one portion of the cross section to anothercan be avoided without difficulty.
~;
The compaction of the sintered body to the ultimate
sintered object can be effected by either hot or cold compres-
sion as already indicated and it has been found to be particu-
larly advantageous to utilize a cold compaction step.
For example, the sintered body can be subjected to cold
pressing in one or more steps. If desired, the so-called co-
axial compac~ion can be used, this being conventional in powder
metallurgy and involving the application of pressure. A material
flow perpendicular to the present direction i5 practically non-
existent when sintered bodies made by the present method areused.
It is a:Lso possible to employ conventional isostatic
presses whereby the sintered body is subjected to pressure while
surrounded or closed, in whole or in part, by elastomeric tools.
The ater-compaction at elevated te~peratuxes can utilize a
closed tool 50 that deterioration at ~wo gaps does not occur.
The machines which are employed are machines of the
type known in the foundry arts as core-forming machines.
Reference may be made to pages 1059 ff. of The Ma]cing, Shaping
and Treating of Steel, United States Steel Company, Pittsburgh,
Pa~, 1971, Preferably core blowing machines or core-sand sling-
ing machines are employed.
In a core blowing machine t the filling of the so-called
core sleeve, which shapes the green compact according tG the
invention when particulate metals are substituted for the sand
and the compaction of the mixture of the particles with the
foundry sand binder, is effected by forming a compressed air-
sand mixture.
12 -
2[3
The core sleeve with the intake opening turned up-
wardly is fixed by mechanical or pneumatically actuated clamping
means to a table. By the lifting of the work table via a fluid-
operated cylinder in the machine stand, the sleeve is pressed
against the nozzle plate which is formed on the bottom of the
sand vessel and has one or more orifices.
Compressed air at 5 ~o 7 bar pressure is introduced
laterally into the sand vessel and an agitator is provided to
form the compressed air/sand mixture. In the ideal case each
individual particle of the sand is surrounded by compressed air.
At the blowing instant the compressed air entrains the
sand through the orifices into the sleeve where the sand is
compacted under its kinetic energy and the compressed-air force.
During the blowing process the compressed air is driven from the
sleeve as it is filled with the sand and special venting open-
ings and passages are provided for thi!3 purpose.
~ When a machine of this type is used in the context of
the process described, the compact form i~ substituted for the
core sleeve or the core sleeve is constituted as the form in
which the compact is shaped and the mixture of foundry sand and
synthetic resin binder is replaced by the metal powder or the
mixture ~hereof with the binder.
A core-sand slinging machine is similar in its basic
elements to the core blowing machine in that it also has a
machine stand, a cylinder elevatabla table, a nozzle plate and
a sand supply vessel.
- 13 -
Th~ filling of ~he core sleeve (as in the case of the
compact form) and the compression of the particular mass is
effec~ed by eeding a prede~ermined quantity of compressed air
with a nominal pressure of 6 - 8 bars into the sand filled
slotted cylinder the mixture expanding therein and acting explo-
sively and in shot-like manner upon the sand column. The sand,
driven at a high velocity, en~ers the sleeve or form between the
machine table and the nozzle plate and is effectively fired into
the latter~
When such a machine is used in the system described,
green compact has high strength and the compact form need not be
maintained under the compressed air pressure. Surplus air is
discharged through the slotted cylinder where it loosens the
remaining sand column without an agitator and is vented through
a valve. Special venting openings and passages can be elimina-
ted provided an upward release of the air is possible.
This machine as well can be used with the metal powders
described. Such machines are known in the art and a more
detailed descrip~ion of them is not considered to be necessary.
In the accompanying drawing the sole FIGURE is a flow
diagram illustrating the principles of an embodiment of the
present invention.
Specific Description
A me~allic powder, generally a prereduced ferrous metal
powder containing a small proportion of copper powder, all of a
particle size below about 600 microns, is fed at
- 14
,,~,
1 to any powder preparation or mixing ~tage 3 which raay be de-
sired w&~n the powder is intimately blended with about 1% by
w~igh~ and a phenolic resin biIIder supplied at 2 and ~s3r~d by
any conven~ional foundry sand ph3nolic b.inder"
The flo~al71e bl~nded mixtur~, ~or which th~ metal parti~
cl~s may have been subJ~c~ed to an oxlda~ion ~rea~m~n~ as ra-
pres~IIted a~ 6 wikh ;:h~ oxidized par~icles suppl~0d at 5, is
introduced in~o a eonventional c :>re blowing or core-sand sling-
ing machin~3 7 in which ~ green c4mpa t is produced in the
lO manner de~cribedO
T~ gre~n complc~" compl~t~ly homog~us in density and
can be self-~upporting, is remov~d from the compact ~orm and
deliv~r2d at 8 ~o a ~intering ~ation 12 which may be supplied
with a reducing gas 9 so ~ r~duction can b~ e~cted.
Th2 6in~ered body at 11 is ~ubjected to fur~her densi~
:1cati4TI, i.eO compaction by forging or pressing at 13 the re-
~ulting powder metallurgical produc~ 14 beillg utilizable direct~
ly i~ de5iredO
It has also b~ell ~ound to be advantag~ous to subj~ct the
20 further eompacted product 15 to a resinte~lng s age 16 and th~n
~ de~ired to fin~l shaping ualder pr~s~ure" the la~ter being
efected iLn a calibration stage 18 to w~lch the sînter~d product
is d~liver~d at 17. The inal powdsr m~tallurgical product can
be recov~red at 19
_-i[l-
~ e
A pistGn rod or the p:Lston of a pass~r~ger vehicle shock
absorber is form~d as ~ sintered productO Th~ gr~3en con~pacts ar~
fornQed from a mixt-lr~ o:E pig :lron powd~r wi~h ~0 by wQight coppe~
30 powder and ~% by weight phenQlic re~in~ Th~ gre~n compac~
-î5-
shaped in a cross-sand slinging machine of the aforedescribed
type with the density of the green compact varied in the axial
direction in accordance with the density desired of the valve
member. The green compact is then sintered at 950C for one
hour in an a~monia cracking gas as a reducing atmosphere. The
oxide free sintered body is then pressed to a density of 6.8 g/
cm3 in a hydraulic press concurrently with the formation of an
annular groove for receiving a sealing ring. To this end an
additional profile is applied in the pressed direction.
The pressed product is then sintered at 1120C in a
belt furnace and then calibrated to yield the finished product.
A strength test shows the ability to take loads of 250 kN.
Example 2
A shock ring for a truck rear axle is fabricated by the
novel method from pig iron powder with 15% grey cast iron powder,
2~ copper powder and l~ phenolic resin (all percentages by
weight). The machine used was a core blowing machine and upon
removal of the green compact at a density o~ 3.8 g/cm3 it is
sintered at 950C for one hour in an ammoniac cracking yas serv-
~0 ing as a reducing atmosphere. The carbon content after reduc-
tion was 0.6~. The sintered compact was densified in a hydrau-
lic press to a density of 7.0 g/cm3 and was found to have an
extremely homogeneous density distribution. The densified
sintered product was the~ resintered at 1120C in a belt furnace
and calibrated. The finished product was found to have a perli-
tic structure and a Brinell hardness of HB 160.
Example 3
A journal bearing with a flange i5 Eormed in a core-
sand slinging machine from a carbon free iron powder containing
~o 1% phenolic resin. The green compact was heated at 950C
- 16 -
J
irl am¢no~aia erac~ g gas and the sln~er2d product was pressed by
an aE~srs:~priakely shaped tool 50 th~ t~ shaft disk wa~
6. 5 g/cm30
~ he d~n~i~ied produc~ w~s sintered in a walking beam fur-
nace a~ 1280C U~illg conv~ntion~ ec~nique~O Th~ Brinell h~rd-
ne~s o~ t~ sleeve was about ~3 45 while ~hat o the flange was
~B ~6.
~ ',
~;~ A thread guide ~or a ~pinning machirle was produced by
rocec75 desc~,~e~
lû sintering in accordaIace with ~h~ ~ The ~ad guide h~d
a configuratian approxi~i~g a cylilnd~r wi~h a mo~e or l~s
~lical groc~ve~, Conv~nt:ional powder m~1:allurgical methods could
~ot be used b~c~use of t~ ~hap~ .
For th~ :Lnner corltour o this ob~ecta a sand cor~ wa~
:~-lr~t m~d~ by cor~ventiorlal four~dry m~hods and was th~n surround~
ed in a cor~ slin~;ing T~chine with a miæture of pig iro~ powd~r
containing 25% by weight grey cast iron powder aad ~U~O by weight
ph~r~ollc resin. The out~r coIltour corr~ponded to the outer
~hape d~s~red"
T~ ~re~ compact was ~ub~ect to 950C for on~ hour
am~aonia cracking gas as a r~ducirlg atmosphere, thl~ slnt~rin~
op~at~on di~playing the islt0~rity o:E sand cor~ so that it could
be r~moved. Th~ sinter~d body wa~ then lnser~ed ill~O separabl~
steel p~ttern cavsr~d with a sllicon ilm a~d o a ~;hapQ compl~
mentary to ~h~ out~r contourO The body wa~ th~n subj~cted to
tatic oompr~siorl such that ~h~ pres~ure was appli~d only
along th0 interior of the ring~, The out~r contour had the pre~
ci~ s~pe de~ired~ The d~ ity of the product after 2ppLic~tion
of a pr~ssure of ~000 bar was abou~ 7.2 g~om3~, Th~ bs~dy was
a~17-
~hen r~sin~ered ~ a crucible furnace at 120~C. The product:
ha~ the desired f~rritic-periliLtlc structure.
18..
